The unstable nature of the RNA molecule enables RNA viruses to evolve far more rapidly than DNA viruses, frequently changing their surface structures. RNA viruses in general have very high mutation rates as they lack polymerases which can find and fix mistakes, and are therefore unable to conduct repair of damaged genetic material. DNA viruses have considerably lower mutation rates due to the proofreading ability of DNA polymerases within the host cell. These mutations of RNA viruses make it more difficult for an organism to develop any kind of lasting immunity to the virus. Because each surviving virus can reproduce itself hundreds or thousands of times, mutations in the RNA sequence occur frequently. It has been estimated that a typical RNA virus may experience alterations of between 0.03 and 2 percent of its entire genome each year thus evolving faster than any other living organism. Mutations occur randomly across the entire length of the viral RNA, and so of course most are not beneficial, producing viruses which lack a needed protein or are otherwise disadvantaged. However, because of the enormous number of offspring produced by each virus, even a high rate of mutation does not threaten the survival of the virus, and when advantageous mutations do occur, they are rapidly selected for and reproduced. This evolution is known as antigenic drift. Thus at least one reason for the lack of suitable vaccines against most RNA viruses is the high rate of mutability of RNA viruses.
The West Nile Virus (WNV) of the Flaviviridae is such an RNA virus for which a vaccine is not available. WNV was first identified in 1937 in Africa and first found in North America in 1999. Migratory birds are considered the primary means whereby infection is spread within and between countries. The virus is transmitted by mosquitoes that have acquired infection by feeding on viremic birds. The virus is then amplified during periods of adult mosquito blood-feeding. Infected mosquitoes then transmit the virus to humans and animals upon feeding thereon.
WNV belongs to the Flaviviradae, a family of over 70 related viruses. WNV is an enveloped single-stranded positive sense RNA virus with a genome of approximately 11 kb encoding for three structural genes and seven non-structural genes.
West Nile Virus is the causative agent for West Nile Virus disease, particularly West Nile encephalitis, predominately in humans, other mammals and birds. The chief concern in both the United States and foreign countries is the lack of effective treatment for West Nile Virus disease. Anti-inflammatory drugs are used to combat swelling of central nervous system tissues, but beyond that no medical intervention is currently available.
The West Nile fever virus also affects horses, particularly in North America and Europe. These horses reveal signs of ataxia, weakness of the rear limbs, paresis evolving towards tetraplegia and death. Horses and camels are the main animals manifesting clinical signs in the form of encephalitis.
The virions of the West Nile fever virus are spherical particles with a diameter of 50 nm constituted by a lipoproteic envelope surrounding an icosahedric nucleocapsid containing a positive polarity, single-strand RNA. A single open reading frame (ORF) encodes all the viral proteins in the form of a polyprotein. The cleaving and maturation of this polyprotein leads to the production of several different viral proteins. The structural proteins are encoded by the 5′ part of the genome and correspond to the nucleocapsid designated C (14 kDa), the envelop glycoprotein designated E (50 kDa), the pre-membrane protein designated prM (23 kDa), and the membrane protein designated M (7 kDa). The non-structural proteins are encoded by the 3′ part of the genome and correspond to the proteins NS1 (40 kDa), NS2A (19 kDa), NS2B (14 kDa), NS3 (74 kDa), NS4A (15 kDa), NS4B (29 kDa), and NS5 (97 kDa).
Recent reports show that WNV can also be passed from human to human by blood transfusion. With the recent epidemic increase in WNV prevalence in the U.S. (CDC, 1999, 2002; Enserink, 2002; Lanciotti et al, 1999), a rise in WNV positive blood donors and rising need for methods to inactivate WNV in blood products can be expected.
Potential vaccines for WNV are described, for example, in U.S. Patent Publication Nos. 2003/0148261A1, 2003/0104008A1 and 2003/0091595A1. Publication No. 2003/0091595A1 describes a WNV vaccine that includes an inactivated whole or subunit WNV. Publication No. 2003/0104008A1 discloses a vector, such as recombinant avipox virus, containing and expressing exogenous polynucleotide(s) from WNV to induce an immune response against WNV. These recombinant WNV vaccines include a vector containing a polynucleotide having a single encoding frame corresponding to, for example, prM-E, M-E and prM-M-E. The vector may include several separate polynucleotides encoding the different proteins (e.g., prM and/or M and E). The vector can also include polynucleotides corresponding to more than one WN virus strain, for example, two or more polynucleotides encoding E or prM-M-E of different strains. Furthermore, the vector can include one or more nucleotide sequences encoding immunogens of other pathogenic agents and/or cytokins. Publication No. 2003/0148261A1 describes various WNV polypeptides and immunogenic fragments for use in WNV vaccines. These vaccines are produced recombinantly using various vectors encoding WNV polypeptides and the vectors are expressed by a variety of host cells.
Methylene Blue (3,7-Bis(dimethylamino)phenothiazin-5-ium chloride), also referred to herein as MB, is FDA approved for oral administration and has been reported to be effective as an antiseptic, disinfectant, and antidote for cyanide and nitrate poisoning. The drug MB has seen limited use to inactivate HIV in blood products (Lambrecht et al, 1991; Mohr et al, 2004).
Further it is known that MB and other phenothiazine dyes (e.g., neutral red, thionine, and toluidene blue) can, in combination with wavelengths of visible light (e.g., 660 nm) inactivate certain viruses (e.g., U.S. Pat. Nos. 6,348,309 and 6,346,529).